Glenn P. A. Yap

A novel pyridine containing self-assembling system: synthesis, characterization, X-ray crystal structure, 13C solid phase NMR and solution studies

Abstract The synthesis of a novel pyridine containing self-assembling system, L, is reported. This system is prepared from the reaction between 2,6-pyridinedicarboxylic acid, [pydc.H2], and 2,6-pyridinediamine, [pyda], in the presence of Et3N in THF as solvent in 88% yield. Double proton transfer from diacid to diamine results in the formation of a self-assembling system consisting of dicationic and dianionic units connecting through H-bonding and ion-pairing simultaneously as shown in the X-ray crystal structure. L is recrystallized from H2O. The crystal system is monoclinic with space group P21/c. One of the carboxylate anions of dianion unit is connected to and directed toward two ammonium cations of dication unit while the other one interacts with neighboring pyridine CH. The characterization was performed using EI, CI, ES mass spectroscopy as well as 1H and 13C solution NMR and X-ray crystal. The solid phase NMR, as a tool for conformation and structure prediction, reveals that the two –CO2− functional groups are not equally involved in the self-assembling system. The 13C solid phase NMR data is in agreement with X-ray crystal structure.

Tetrametallic Reduction of Dinitrogen: Formation of a Tetranuclear Samarium Dinitrogen Complex.

The cooperative attack of four (dipyrromethanyl)Sm(II) units on dinitrogen resulted in a novel tetranuclear samarium dinitrogen complex (shown schematically). The presence of halogen atoms inhibited reactivity with dinitrogen through the assembly of divalent samarium clusters. dipyrr=diphenylmethyldipyrrolide dianion.

Synthesis and structural characterization of the first trialkylguanidinate and hexahydropyramidopyramidinate complexes of tin

Abstract The first guanidinate complexes of tin have been prepared using N,N′,N′′-trialkylguanidinates ([(RN)2C(NRH)]−; R=cyclohexyl; isopropyl) and 1,3,4,6,7,8-hexahydro-2H-pyramido[1,2-a]pyramidinate (hpp−) as ligands. The direct reaction between triisopropylguanidine and SnCl4 provided the complex {[iPrN]2C[NHiPr]}SnCl3 (1) along with concomitant formation of the guanidinium salt {C[NHiPr]3}+[SnCl5(THF)]− (2). The Sn(II) guanidinate complexes {(C6H11N)2C[NH(C6H11)]}2Sn (3) and {CN[N(CH2)3]2}2Sn (4) were prepared through metathesis reactions between 0.5 equiv. SnCl2 and (C6H11N)2C[NH(C6H11)]Li or hppLi, respectively. Complex 4 is the first reported mononuclear complex of this ligand. In contrast, the reaction of hppLi with 1 equiv. SnCl2 afforded a bridging dinuclear species, {CN[N(CH2)3]2SnCl}2 (5). A second mononuclear complex of the hpp− ligand, {CN[N(CH2)3]2}2SnCl2 (6), was the product obtained from the reaction of 2 equiv. of hppLi with SnCl4. The full structural details of compounds 1 and 3–6 are reported. In the case of compounds 1 and 3 these results revealed a distinctly unsymmetrical bonding mode for the bidentate guanidinate ligand and suggest variable degrees of π delocalization with the ligand. The geometries of the Sn centers in 3, 4 are derived from distorted trigonal bipyramidal coordination with a stereochemically active lone pair occupying one coordination site. In contrast, complex 5 displayed a geometry derived from a tetrahedral ligand array with one vertex occupied by a lone pair of electrons. Complex 6 is six coordinate and possesses 2 equiv. chelating bidentate hpp− ligands and two cis-chloro groups.

An effective synthesis of alkyl β-cyano-α,γ-diketones using chlorosulfonylisocyanate and a representative Cu(II) complex

Abstract Chlorosulfonylisocyanate, a source of electrophilic cyanide equivalent, was used for the synthesis of three β-cyano-α,γ-diketones. The reactions proceeded in a straightforward fashion and the desired organic compounds were isolated in high-yield and excellent purity. The ligands then yielded homoleptic Cu(II) coordination complexes stabilized by intermolecular contacts. This is illustrated in the X-ray crystal structure of bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II).

Reversible Fixation of Ethylene on a SmII Calix-Pyrrole Complex

Reversible ethylene fixation in lanthanide chemistry is demonstrated by the SmII derivatives [R8 -calix-pyrrole)(Et2 O)Sm{Li(thf)2 }{Li(μ3 -OCH=CH2 )}] (R=Et, {-(CH2 )5 -}0.5 ), which react with ethylene to afford the corresponding dinuclear complexes (see picture).

The Synthesis of a Novel Strained Diyneparacyclophane and Its Dimer by Metal‐Mediated Coupling

Relieve strain with a twist! Synthesis of the paracyclophane 1 and its dimer 2 employed a sequence of metal-mediated couplings. The X-ray analysis of 2 revealed a helical twist inherent in this structure, which created extended arms, that trapped a molecule of solvent. A carboxylic acid derivative of 1 was also prepared, and its structure indicated the diyne rod moiety of 1 is distorted more than in analogous compounds.

The interconversion of formic acid and hydrogen/carbon dioxide using a binuclear ruthenium complex catalyst

The complex [Ru2(μ-CO)(CO)4(μ-dppm)2] in acetone solution is an efficient catalyst for the reversible reaction between formic acid and hydrogen/carbon dioxide. Complexes identified during the catalytic reactions include the hydrido and formato complexes [Ru2(μ-H)(μ-CO)(CO)4(μ-dppm)2]+, [Ru2(μ-HCO2)(CO)4(μ-dppm)2]+, [Ru2(μ-H)2(CO)4(μ-dppm)2], [Ru2H(HCO2)(CO)4(μ-dppm)2] and the coordinatively unsaturated [Ru2H(μ-H)(μ-CO)(CO)2(μ-dppm)2].

Crystal structure of the phosphanylidene-σ4-phosphorane DmpPPMe3 (Dmp=2,6-Mes2C6H3) and reactions with electrophiles

Abstract The stable phosphanylidene-σ4-phosphorane DmpPPMe3 (1, Dmp=2,6-Mes2C6H3) has been examined by single-crystal X-ray diffraction methods. The structure of 1 features a relatively short PP bond length of 2.084(2) A. Reactions of 1 with various electrophiles demonstrate the nucleophilic behavior of the phosphanylidene atom of 1 and also provide access to new organophosphorus compounds. For example, addition of excess BH3 (in the form of either BH3·THF or BH3·SMe2) to 1 leads to formation of a mono-borane adduct DmpP(BH3)PMe3. Reactions of carbon and silicon based electrophiles EX (E=R3C or R3Si; X=halide or OTf−) produce either diphosphanium salts [DmpP(E)PMe3]X or phosphines DmpP(E)X. In some cases equilibrium mixtures of both product types are observed, and the equilibria can be shifted by addition of either X− or PMe3. Compound 1 is also readily protonated by HOTf, HCl and PhOH. As found for the carbon and silicon based electrophiles, the nature of the resulting product depends on the counterion.

The kinetic instability of σ-bound aryloxide in coordinatively unsaturated or labile complexes of ruthenium

Abstract Reaction of RuCl2(PPh3)3 (1) or RuHCl(PPh3)3 (2) with KOAr (Ar=4-tBuC6H4) in non-alcohol solvents affords π-aryloxide derivatives Ru(η5-ArO)(o-C6H4PPh2)(PPh3) (3a) or RuH(η5-ArO)(PPh3)2 (6a), respectively. The phenoxide analogues 3b and 6b are obtained on use of KOPh or TlOPh. Treatment of 1 with 1 equiv. KOAr in the presence of isopropanol liberates the phenol and acetone, affording clean 2 in quantitative yields. In 3:1 methanol–CH2Cl2, RuHCl(CO)(PPh3)3 (4) is also formed in small amounts. Reaction of 1 with 2 KOAr in 20% MeOH–CH2Cl2 affords a mixture of 6a and RuH2(CO)(PPh3)3 (5). In the corresponding reaction of 2 with 1 KOAr, σ–π isomerization of the σ-aryloxide ligand dominates, affording 6a·MeOH as the principal product. Treatment of 6a with ethereal HCl gives [RuH(η6-ArOH)(PPh3)2]Cl (7a); the corresponding reaction of 6b yields RuCl(η5-PhO)(PPh3)2 (8b). The crystal structures of 3a, 3b, 4, 5, 7a, and 8b are reported.

An Attractive Route to Olefin Metathesis Catalysts: Facile Synthesis of a Ruthenium Alkylidene Complex Containing Labile Phosphane Donors

Reaction of RuHCl(PPh3)34 with 3-chloro-3-methyl-1-butyne effects transformation into RuCl2(PPh3)2(CHCHCMe2) 1c. Starting 4 is available commercially, or via quantitative reaction of RuCl2(PPh3)3 with one equivalent of alkali phenoxides or isopropoxides in refluxing benzene-2-propanol. Phosphane exchange between 1c and PCy3 or 1,3-(CH2PCy2)2C6H4 is rapid at RT, affording RuCl2(PCy3)2(CHCHCMe2) 1b or the novel alkylidene complex RuCl2[1,3-(CH2PCy2)2C6H4](CHCHCMe2) 7. Much slower exchange occurred on use of RuCl2(PCy3)2(CHPh) (1a) as precursor. Complex 1c is stable indefinitely (months) in the solid state at RT under N2, but dimerizes slowly in solution to give RuCl(PPh3)2(μ-Cl)3Ru(PPh3)2(CHCHCMe2) 6a. 2,7-Dimethyl-octa-2,4,6-triene, the formal product of carbene coupling, is observed by 1H NMR. Dimerization does not compete with phosphane exchange. A side-product arising from use of excess 3-chloro-3-methyl-1-butyne in the synthesis of 1c was identified as Ru(IV) carbyne complex RuCl3(PPh3)2(≡CCHCMe2) 5, the structure of which was confirmed by X-ray crystallography.